A death row inmate whose lawyer and family claim has been demonstrably mentally retarded since his early teenage years will get a new chance to prove it in federal court, the 5th U.S. Circuit Court of Appeals ruled Tuesday.

A three-judge panel ruled there was enough evidence presented that lower courts may have relied on the testing and conclusions of a controversial Fort Worth psychologist to give John Matamoros of Houston a fresh start in a claim that, if successful, would spare him the death penalty.

In granting a "certificate of appealability," the judges said that Matamoros should have the same chance to prove retardation as other inmates who had been evaluated by George Denkowski, who testified frequently for Texas prosecutors after the U.S. Supreme Court outlawed capital punishment for the mentally retarded in 2002. Denkowski's unconventional methods drew the ire of defense attorneys who said he was a purveyor of junk science and brought a reprimand from the state licensing board.

Appellate scrutiny

As part of a settlement with the board, Denkowski stopped testifying in capital cases. As word spread of his questionable approach, the cases in which he was involved have received heightened appellate scrutiny.

Matamoros was convicted of the murder of Edward George Goebel during a 1990 burglary of his home. His lawyer, Stanley Schneider, does not contest Matamoros' guilt but argues that he was exactly the sort of defendant that the Supreme Court sought to protect in its Atkins. v. Virginia decision.

Schneider said the evidence at trial painted Matamoros as a dysfunctional, intellectually challenged man who failed academically from his earliest days, was endlessly teased for being "dumb" by classmates as a youth, never made it to high school, showed such poor personal hygiene that for many years he required help bathing and cleaning up after going to the bathroom, and came from a family with many mentally challenged members.

Trouble started early

Easily manipulated by others and seeking approval through criminal acts such as stealing cars, Matamoros got into trouble with the law as a teenager. He was diagnosed as mildly mentally retarded at 14 by a psychologist hired by juvenile authorities.

"Three psychologists looked at him post-Atkins and said he was mentally retarded," Schneider told the Chronicle in 2011. "A doctor who tested him when he was 14 said he was mentally retarded. On the other side is Denkowski.''

Denkowski discounted Matamoros' history and previous evaluations in favor of his own criteria, which included tests for so-called adaptive behavior, which he insisted proved that Matamoros could perform at a higher level than his academic or medical records suggested. Matamoros was sentenced to die by a Harris County jury.

The 5th Circuit panel did not rule on the merits of Matamoros' claim of retardation, granting him only the right to make the claim in subsequent appeals.